title: Point-of-care bedside gas analyzer: limited use of venous pCO2 in emergency patients.
abstract: BACKGROUND
  Because arterial punctures are more painful, venous blood gas analysis has been proposed as an alternative.
  
  
  OBJECTIVE
  To determine if venous pCO(2) can replace arterial pCO(2) in emergency patients using a bedside blood gas analyzer.
  
  
  METHODS
  This is a cross-sectional study. We recruited patients who were deemed by the attending Emergency Physicians to require arterial blood gas analysis to determine their ventilation or acid-base status. A venous and an arterial blood gas sample were drawn from the patient, temporally as close to each other as possible. Both samples were then analyzed using the same bedside blood gas analyzer immediately after collection.
  
  
  RESULTS
  There were 122 paired samples obtained. The strength of the association between arterial and venous pCO(2) is r = 0.838 (p = 0.001). The Bland-Altman bias plot methods for agreement show a mean difference of 3.3 mm Hg with two standard deviation limits of agreement being -17.4 to 23.9; 93.4% of the pCO(2) values fell within two standard deviation limits. Venous pCO(2) below 30 mm Hg had a 100% (95% confidence interval [CI] 90.5-100) sensitivity and 100% (95% CI 80.7-100) Negative predictive value to rule out hypercarbia, defined as arterial pCO(2) > 45 mm Hg.
  
  
  CONCLUSIONS
  There is significant variability in the arteriovenous difference of pCO(2) readings, hence, arterial punctures are still needed to specifically determine the arterial pCO(2).
authors.affiliation: Department of Emergency Medicine, National University Hospital, Singapore.
authors.forename: Irwani
authors.initials: I
authors.lastname: Ibrahim
authors.forename: Shirley B S
authors.initials: SB
authors.lastname: Ooi
authors.forename: Chan
authors.initials: C
authors.lastname: Yiong Huak
authors.forename: Sunil
authors.initials: S
authors.lastname: Sethi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001158:Arteries; D001784:Blood Gas Analysis / Q000295:instrumentation*; D001800:Blood Specimen Collection / Q000379:methods; D002245:Carbon Dioxide / Q000097:blood*; D003430:Cross-Sectional Studies; D004635:Emergency Medicine / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D019095:Point-of-Care Systems; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D014680:Veins
chemical_list: D002245:Carbon Dioxide